Fin configuration for fin and tube heat exchanger



J. W. B. LU

June 2 1970' FIN CONFIGURATION'FOR FIN AND TUBE HEAT EXCHANGER ,Filed July 17, 1968 7.. Z J. .w m m United States Patent 0 3,515,207 FIN CONFIGURATION FOR FIN AND TUBE HEAT EXCHANGER James W. B. Lu, Greendale, Wis., assignor to Perfex Corporation, Milwaukee, Wis., a corporation of Wisconsm Filed July 17, 1968, Ser. No. 745,549 Int. Cl. F28d J/04 U.S. Cl. 165-151 12 Claims ABSTRACT OF THE DISCLOSURE In a heat exchanger having an arrangement of fins and tubes the fins are provided with corrugations which surround the tubes. The corrugations are diamond-shaped with respect to flow over the fins and past the tubes.

BACKGROUND OF INVENTION Field of the invention This invention relates to heat exchangers and, more particularly, to a fin and tube type exchanger and a fin configuration for effectively directing air flow around the tube.

Description of prior art In a fin and tube type heat exchanger, for example a refrigerator core, heat transfer is to be effected between a medium flowing in the tubes and one flowing externally over the tubes and fins. Heat transfer occurs directly from the medium within the tube to the external medium and the fins are provided to increase the effective heat transfer area. Heat transfer from a fin is dependent upon the thickness of the boundary layer of the medium flowing over the fin and can be improved by reducing the boundary layer thickness. One heretofore accepted manner of reducing boundary layer thickness has been to create turbulence in the external medium by agitating flow; however, such agitation can have a countervailing, undesirable effect of sharply increasing resistance to flow,

Flow over a tube tends to separate at or near the mid-line of the tube leaving a relatively quiescent area on the downstream side of the tube. This is undesirable from a heat transfer standpoint. First, it reduces the amount of direct heat transfer between the tube and external medium and, secondly, it creates a relatively low velocity region immediately downstream of the tube which results in a relatively thicker boundary layer on the fin in that area. In a turbulent application, or artificially turbulent application as mentioned above to reduce the boundary layer thickness, this lower velocity on the downstream side of the tube can result in a substantially thicker boundary layer on the fin and markedly reduced heat transfer as compared to that on the upstream side of the tube.

This invention is concerned with the problem of achieving effective flow of the external medium through a fin and tube type heat exchanger, i.e. reducing boundary layer thickness on the fin and positively directing external flow over the entire tube surface and doing so without adversely affecting external flow.

Various proposals have been made in the past for directing or influencing flow in a fin and tube heat exchanger. Undulating or wavy fins have been proposed to create turbulence. Also, specific fin configurations have been proposed to direct the external flow relative to the tubes, examples of such arrangements are found in US. Pats. 1,957,292, 2,217,469 and 3,249,156. These configurations have generally been deficient as being unduly complex, as requiring structural elements in addition to the basic fin and tube elements, as requiring involved fabricating procedures, as offering excessive resistance to flow of the external medium and/ or as not effectively directing the flow external to the tubes.

SUMMARY OF INVENTION A general object of this invention is to provide an effective and relatively simple to fabricate arrangement on the fin, or fins, of a fin and tube type heat exchanger which reduces the fin boundary layer thickness and positively directs flow around the tubes.

For the achievement of this and other objects, this invention proposes the use of continuous surfaces extending on the downstream side of the tubes and effective to direct flow past the tubes over the downstream side of the tubes. In its more specific aspects the continuous surfaces are provided by corrugations throughout the fins.

DESCRIPTION OF DRAWINGS FIG. 1 is a perspective of a portion of a fin and tube arrangement;

FIG. 2 is a plan view of the fin and tube arrangement of FIG. 1;

FIG. 3 is a section view through a section of a fin and tube assembly as taken relative to the fins generally along a line such as 3-3 in FIG. 2; and

FIG. 4 is a section view of the fin and tube assembly generally along a line such as 4-4 in FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT In a fin and tube type heat exchanger for example a refrigerator core, a number of tubes extend through each fin. The fin closely fits the outer tubewall and is provided to increase the effective heat transfer surface. A number of parallel, closely spaced fins are: used and air, the external medium referred to above, is directed between the fins and over the tubes to effect a heat transfer between the air and the refrigerant flowing through the tubes. This invention will be described as embodied in a refrigeration core but it is not necessarily limited to such an environment.

For convenience, only a portion of the heat exchanger core has been illustrated in the drawing, that is one fin 10 and three tubes 12 in FIG. 1. It will be appreciated that more tubes are used as are a number of similar or identically formed fins, moroever an in line arrangement of tubes can be used as well as the staggered arrangement illustrated.

As stated above, the fins tightly engage the tubes to increase the effective heat transfer surface. A refrigeration medium flows in the tubes and air is directed over the fins. A transfer of heat occurs between the flowing air and the tubes and fins. Assuming flow in the direction of the arrows in FIGS. 1 and 2, the air flow will impinge directly on the upstream portion of the tubes but will have a tendency to separate at or near the mid-line of the tube, with respect to air flow, creating a relatively quiescent area on the downstream side of the tube where the air does not engage the tube. One of the factors in determining the amount of heat transfer from the fins is the thickness of the boundary layer of the air flowing over the fins and common practice has been to provide some means of creating turbulence on the fin surface which has the effect of reducing the boundary layer thickness. This invention solves both the problem of reducing boundary layer thickness and positively directing air flow to the downstream side of the tubes by imparting a particular corrugated configuration to the fin.

Pin 10 is generally planar and is provided with a particular pattern of corrugations such that, with respect to the air flow over the fin and past the tubes, each tube is surrounded by a diamond-shaped surface. More particularly, the fin is provided with a number of flat surfaces 14 which define a plane, this being the normal plane of the fin before the corrugations are formed. Each of the surfaces 14 is provided with an opening 16 for receipt of a tube 12. The corrugated pattern is provided by suitably deforming the fin such that the corrugations project from the normal plane of the fin, surfaces 14. structurally, the corrugations provide indentations in one of the surfaces of the fin and projections from the opposite fin surface. Each corrugation includes upstream angularly related V-shaped surface portions 18 and 20 which diverge from a common end 21 upstream of the tubes to approximately the midline of the tube at which point they are connected to downstream V-shaped portions 22 and 24. The downstream portions converge to a common end 25 on the downstream side of the tube. The corrugations in addition to being V-shaped on both the upstream and downstream sides of the tube are also V-shaped in crosssection which is effective to cause the air to follow an undulating path. The diamond-shaped corrugations are identical both in construction and in their relation to their respective tubes and hence only one has been described and identified with regard to its respective tube.

It will be noted in FIG. 2 that the corrugation pattern, and the indentations thereof, extend over virtually the entire surface of the fin, and correspondingly the projections extend over virtually the entire opposite surface of the fin. With the diamond-shaped configuration and with the downstream portions 22 and 24 extending from generally the midline of the tube on opposite sides thereof where the air flow would normally separate from the tube, the downstream corrugation portions 22 and 24 interrupt and direct the air flow around to the rear of the tubes. This has a two fold effect, it brings the air directly into contact with the downstream side of the tube thereby achieving heat transfer from an otherwise lost surface. Secondly, it prevents the creation of a quiescent area downstream of the tube and reduces excessive boundary layer thickness which might otherwise occur in that area. This configuration pattern increases the overall heat transfer of the fin and tube arrangement and does so without adversely affecting air flow through the core.

It will also be noted that with the corrugation pattern also providing projections on the opposite side of the fin surface, the projections further cooperate in achieving the positive direction of the air flow around the tube. Moreover, this is achieved with virtually an imperforate fin which does not reduce fin efficiency by breaking the path of conduction.

When a number of fins are assembled in making up the core they assume the position illustrated in FIGS. 3

and 4. The corrugation projections on one end fin are opposed to the corrugation indentations on an adjacent fin and vice versa, and the diamond-shaped corrugations of adjacent fins overlie and are in alignment with one another. Collars 26 are provided at each fin opening to enhance the heat transfer connection between the fins and tubes. These collars also act as spacers, each collar engaging a flat surface .14 at a tube opening in an adjacent fin, thereby insuring an open passage for air fio'w between the fins. With this arrangement air flow is confined between adjacent fins, with the aligned diamond-shapes and opposed projections and indentations resulting in more positively directing air flow around the tubes. The opposed, aligned projections and indentations positively direct the air flow along an undulating path, this produces some air turbulence to reduce boundaiy layer thickness but with a minimum of resistance to flow.

It will be appreciated that a number of fins are generally used and all have the same general relation as that of the two fins illustrated in FIGS. 3 and 4. It will also be appreciated that generally the fin and tube arrangement 4 is supported in a frame, or the like which serves to better define a flow path over the fins in the direction of the arrows in the drawing. The frame, or the like, cooperates to define an inlet and outlet through which air flow occurs. Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

I claim: 1. In a heat exchanger adapted for fluid flow in a given direction therethrough and comprising, in combination,

a tube, a fin including means defining an opening through said fin, said tube disposed in and extending through said openand means defining a surface extending continuously in surrounding relationship with and around said tube and operative to direct at least a portion of said fiow over said fin around said tube to and for flow over the downstream portion of said tube. 2. The heat exchanger of claim 1 wherein, with respect to said flow, said continuous surface is generally diamond-shaped.

3. The heat exchanger of claim 2 wherein said fin is imperforate except for said opening,

and said diamond-shaped surface comprises an indentation in said fin. 4. The heat exchanger of claim 2 wherein said fin is a generally planar member having oppositely facing surfaces, and said diamond-shaped surface is displaced from the general plane of said fin comprising a diamond-shaped indentation in one of said fin surfaces and a diamondshaped projection on the other of said fin surfaces.

5. The heat exchanger of claim 2 including a plurality of said tubes, wherein a plurality of said openings are defined in said fin and with said tubes disposed in and extending through said openings, and wherein said diamond-shaped surfaces for deflecting flow around said tubes are provided at and surround each of said tubes. 6. The heat exchanger of claim 5 wherein said fin is a generally planar member having oppositely facing surfaces,

and said diamond-shaped surfaces project from the general plane of said fin and each comprises a diamondshaped indentation in one of said fin surfaces and a diamond-shaped projection on the other of said fin surfaces. 7. The heat exchanger of claim 6 including a plurality of fins each being generally planar with oppositely facing surfaces and having diamondshaped surfaces projecting from the general plane of each of said fins and surrounding said tubes, said diamond-shaped surfaces comprising a diamondshaped indentation in one of said fin surfaces and a diamond-shaped projection on the other of said fin surfaces, wherein said tubes extend through said fins, and wherein adjacent fins are spaced apart and the indentations of one fin are opposed to the projections of an adjacent fin and the diamond-shapes of ad jacent fins are in relative alignment. 8. The heat exchanger of claim 5 wherein said fin is a generally planar member and is provided with corrugations over substantially its entire surface, and wherein said corrugations provide said diamondshaped surfaces at said tubes. 9. In a heat exchanger adapted for fluid flow in a given direction therethrough and comprising, in combination,

a tube,

a fin including means defining an opening through said fin,

said tube disposed in and extending through said opening,

and means defining continuous surfaces at said tube, said continuous surfaces converging angularly from areas on opposite sides of said tube to a common area on the downstream side of said tube for interrupting a portion of flow over said fin and directing said flow portion around said tube to the downstream portion of said tube.

10. The heat exchanger of claim 9 wherein said fin is a generally planar member having oppositely facing surfaces,

and wherein said continuous surfaces comprise indentations in one of said surfaces and projections on the other of said surfaces.

11. The heat exchanger of claim 10 including a plurality of said tubes,

wherein said fin includes a plurality of said openings with said tubes disposed in and extending through said openings,

and wherein said fin is provided with corrugations over substantially its entire surface with said corrugations providing said continuous surfaces at each of said tubes.

12. The heat exchanger of claim 10 including a plurality of tubes and a plurality of fins through which said tubes extend, each fin being generally planar with oppositely facing surfaces and having said continuous surfaces at each of said tubes and projecting from the general plane of each of said fins,

said continuous surfaces comprising indentations in one of said fin surfaces and projections on the other of said fin surfaces,

and wherein adjacent fins are spaced apart and the indentations of one fin are opposed to the projections of an adjacent fin and the angularly converging surfaces of adjacent fins are in alignment and converge in a common direction.

References Cited UNITED STATES PATENTS 1,553,093 9/1925 Modine 165151 1,920,313 8/1933 Mautsch l-151 1,927,325 9/1933 Ritter -151 FOREIGN PATENTS 5,388 l/l906 France.

25 ROBERT A. OLEARY, Primary Examiner T. W. STREULE, Assistant Examiner 

